The cost of a mattress generally precludes frequent replacement by the average person, and repair is generally not practical. As a mattress undergoes normal usage, it begins to sag where it is frequently used, to develop uneven spots and also presents a nonuniform response to body weight. Such defects frequently occurs in the padding which forms and defines the upper surface of the mattress. Higher priced mattresses can become subject to the same difficulties, even though higher quality mattresses will have substantially more coils and be better supported and constructed. With any innerspring mattress, the combination of surface padding and interior springs is intended to provide both some degree of softness to the touch and adequate resilient conformity to the contours of the user's body, in accordance with desired firmness. Both factors are highly desirable for sleeping comfort. Even a person who wishes very firm support, for example, does not wish to be in direct contact with rigid surfaces which can quickly cause discomfort particularly to arms and hands when body weight rests upon them. As both padding and interior structure deteriorate with wear and usage of a mattress, however, there can be a substantial increase in discomfort because of changes in either or both of the surface response and body support functions.
Different techniques are widely used for providing limited improvements in mattress defects. Mattress pads, generally of thin quilted fabric, are employed primarily to supply a protective covering for mattresses. They concurrently act to increase the surface padding thickness slightly although there is neither appreciable softness or support, and they tend to become locally compressed or matted quite rapidly. Thin panels may be inserted for orthopaedic reasons above or below the mattress to provide greater firmness, but such expedients are directed only to limited functions. Foam pads have been superposed on mattresses, but foam pads of themselves when used in adequate thicknesses have a springy characteristic and a lateral shifting tendency that change the mattress response so that it has substantially more of a floating characteristic, which many people do not like. The need for a low cost, readily maintainable bedding unit of general applicability that provides conversion of a stiff, worn or sagging mattress to the more luxurious response and support of a high quality mattress, still remains.